Death Stranding - Because I still remember so many details about that world: the topography; safehouse locations; where a river was shallow enough to traverse with or without tools; safe routes up and down mountains; even the player-placed bridges and the like became landmarks by which I could orient myself. The Balance mechanic while walking forced me to look at the world in detail, and as a result I came to remember and appreciate it for its beauty to an incredible extent.
Followed by Days Gone probably, because I really loved how it took the tried and true AAA open world design of camps and side quests and tying them, more often than not, to storylines and characters. To give it a piece of story, some relevance. I felt more compelled to complete everything in DG than I have in an open world game for years because it managed to make it seem like the people around me truly needed my help. It's one of the few open world games where I did take my time to listen to conversations going on in the camp.
3rd would be Tsushima because I was quite a fan of how its open world was full of random events, especially on the roads. Mongol patrols, supply caravans, hostage situations... felt very lively. Having the wind be what guides you felt really cool too. No waypoints also meant a great opportunity to get lost and find some unintentional hijinx and conflict along the way. There is some repetition, but the locations you discover are quite varied. There are bandit camps, but there are also little shrines to meditate at, cool platforming challenges, some beautifully quiet moments in the open world.
